A known typical valve for controlling supply of a fluid is disclosed in, for instance, Patent Literature 1. This valve includes a valve seat, a valve body in the shape of a circular plate being seated on the valve seat to close a channel, an arm extending from a surface of valve body in a flow direction of the fluid, and a valve shaft extending in a direction orthogonal to the flow direction and connected to a distal end of the arm. The valve shaft of the valve is axially actuated by an air cylinder to rotate the valve body around the valve shaft, thereby opening and closing the channel. The valve shaft is eccentric to a straight line orthogonal to a center axis of the channel, so that the valve body is pressed hard against the valve seat to enhance sealing performance.